Allow the brush settings lists to respond to drag inputs

Within the brush settings interface, there is the brush options list and also the brush sensors lists nested within them. Due to the small sizes of these list items, it is not too difficult to accidentally drag the pen across multiple options/sensors when attempting to select one. Currently, in such a case, Krita effectively ignores the input.

This commit makes it so that dragging the mouse/pen across these options/sensors will now effectively select the last highlighted option/sensor, instead of doing nothing.

This effectively fixes BUG:425526 as this commit ensures the correct curve is displayed by selecting the last highlighted sensor.

Test Plan

Drag click across multiple brush options/sensors, and observe the highlighted and selected option/sensor.

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.